In assembly, there are a lot of names already used, many of them are even single letters. Since you can't reuse variable names that are already in use, PBP places an underscore in front of all variables declared in your program to eliminate possible contentions.

While working in PBP those underscores are transparent, because PBP adds them when needed. But at the ASM level, you have to add the underscore to the PBP variable name to be able to access it.

In the case of _PicOSC, it just retrieves the value of the DEFINE OSC XX for use in calculating the amount of time used by the statements.
The OSC value is not directly available in PBP.

Did I miss it?
Section 8.2 Programming in Assembly Language
Page 180 in the latest manual.

hth,